Ok - I know this is one of the most beat up and cryptic topics so I've finally came up with an answer through experience. My setup is the one that seems to have this question come up most often - sbc with early intake with breather on filler and smooth valve covers. Before anyone wastes time it doesn't work. These are my findings: First off the oil got dirty after approximately 10 hours of driving. After that i blew out my front and rear intake seals and sprayed down my car pretty well with a fine oil mist kicked up by the fan on a 1 hour highway trip. This motor only has about 5k on it and has excellent compression and very little blowby. Still it makes enough crankcase pressure during acceleration to cause a problem. Bottom line is YOU NEED TO RUN A PVC FOR THE SYSTEM TO WORK PROPERLY. A single vent is not enough!!! I ended up gutting my breather to let the engine breath a little better for the time being. I'm leaving tomorrow for the Jump and JIve in Asbury, NJ (this Saturday) so i don't have time to whip up a solution. Once i get back i'll rework my system. I'll probably going to do a corvette style filler tube with the PVC fitting and vent to a breather hidden in an old chevy oil filter canister out of one of the valve covers. That or machine a hole in the intake for a pvc grommet. In case you didn't get the message: RUN A PVC! Hope this save somebody some grief.
sorry to nitpick, but it's pCv valve - positive crankcase ventilation valve, not pVc- polyvinylchloride
It may well be an engine problem. I've run most everything without a PCV, just open breathers and never had more than just a tiny oil misting. If you're spewing as much oil as you say...why do you assume there isn't much blow by?
Road draft tube or PCV valve, take your choice, but short of a drag race only pan evac system you need one or the other. Early intake on late motor without provision for a road draft tube? Use the filler tube that has a PCV valve attached, just make sure you rig up a breather somewhere else on the motor to get air into the crankcase. Flow should be across the crankcase to minimise pockets of vaper, but a breather cap toward the rear of either rocker cover should work admirably.
I just installed finned valve covers on my 80 sbc with offy breathers on each one and got rid of the pcv ,drove 75-80 mph to socal and back 3 1/2 hr. each way with only a small drip on each one.
ive run without a PCV valve for the last three years, got cal custom valve covers with no breathers and only a breather on my intake - dont get any oil pushing out gaskets or have blown any gaskets out. also dont get dirty oil. only think i get is a very light mist of oil from engine once im going more than 50/60mph. engine was rebuilt using 10.5:1 pistons and a cam so its all new. had the heads of since this setup was put in and all the piston tops and the heads were really quite clean - cleaner than i though. plugs are also pretty clean so dont think im getting a lot if any blow by. if its blowing out your instake gasket seals sounds like you have other issues...
I have a front filler/breather tube and a rear road draft tube and it sprays oil, especially on long road trips.. been thinking of connecting a hose to the end to run it to the rear of the car
On my 327 we ran the breather tube into the exhaust pipe. Put a 45 degree angle on the pipe so the exhaust would suck it out. 10,000 miles with no problems.
I have a late model block, early intake with fill and breather, no hole valve covers and have no trouble at all with the exception of a tiny mist of oil out of the breather at speed. That was fixed with a 99 cent wrist band/sweat band over the breather cap. It is a new motor, the oil has been changed twice and it is super clean when changed. I believe you may have other issues. Did you use the rubber intake gaskets or did you RTV the ends of the intake.
Just drill the back of your intake and put a pcv valve there. Edelbrock makes a manfold just like that which you can use the front fill tube with it. I ran that combo for years with zero problems. Bill
....or, most carburetors have a pipe threaded provision for power brake vacuum on the rear of the base. If you're not running a power brake booster, you can plumb a PCV valve there.
On my flattie I use a PCV, mine like every other flattie has a fair amount of blow by. I have capped off my fuel pump stand (running electric) put a PCV in the block off plate and ran a tube down to the exhaust. I have placed a Y-tap into the exhaust. As the exhaust passes the Y it sucks the crankcase fumes into the exhaust and burns up whatever oil may be in it. No oil spatter anywhere! Works great, just make sure to use heat resistant tubing!!!!!
You probably don't want to do that. The road draft tube is designed to scavange the crankcase vapors out of the engine, to keep fresh air moving through the insides. If you connect a hose to it or modify it you defeat it's purpose. Block the tube install a pcv in it routed to your intake manifold. A search of the archives should get you all you need to know. Terry
I run a PCV and a single breather of course I've got mine setup in the rocker covers becuase I really don't care what everyone thinks and have a hood. To do it right you either need a pcv and at least one breather, or a road draft tube and one breather. They make a PCV valve that's made to lay on its side. You can plug it into the side of the rocker cover. only the nost hard core " Your car isn't trad" type is going to really notice it. Personaly I think those types can take an aeronautical intercourse at a tumbling piece of pastry. I build as close as I can but I gotta make some provisions to make me happy and one of those is running like a turpentined cat.
An oil fill tube from a mid year 64-67 corvette has a nice provision for a pcv valve in it. Looks cool - works cool - is cool
My nephew brought me a junk plymouth trailduster 4x4 with a v8 not long ago. It had after market valve covers on it and a pcv valve but something was wrong. His oil was foaming on the dipstick. I told him somehting is not venting right. I rerouted a bunch of vacuum lines and found the pcv hose was cappe doff with a plug on the carb so I pulled the cap off of it and reattached still had foamed oil. He drove it a little like that and I took the carb off to clean i tout and check it. Someone put bondo in the bottom of the carb blocking the inside passge of the pcv vacuum takeoff. I drilled that crap out and now his oil is fine and it runs better.
So tell me....why would not running a PCV cause your oil to get dirty quickly? How do you know that you don't have blowby? I have a BBC with 145K on it and it has tons of blowby, and still has an even 195psi on all cylinders. Compression doesn't mean that you don't have blowby. Not running a PCV is fine as long as you vent the crankcase somehow. It is harder on older engines with more blowby. You really want to have a negative crankcase pressure, not just neutral, and an open breather won't get that, but a road-draft tube, PCV, or exhaust scavenge system will. So pick your poison, any of them work setup correctly.
The hose from the Carb goes to a PCV on the oil filler tube ... On the the of the rear ( where a road draft tube was ) the is a nipple with a hose to go to the air cleaner ... like factory 67 Novas and Corvettes ... .
My '56 Desoto had a draft tube coming out of the rear of the valley pan. I removed that, stuck in a grommet and ran a PCV to the back of the carb. My Buick straight 8 has a draft tube coming off the side push rod cover. I drilled a hole into the top of the draft tube baffle added a grommet and pcv hooked into the wiper vacuum line. I also but a rubber plug (like a wine cork) inside the top of the draft tube to block it off. I haven't driven this much since but it has good manifold vacuum...
I don't run a PVC calve on my 350cid SBC or my 512cid caddy, just breathers on the valve covers! Never had a problem! No blown gaskets, I do replace the breathers after about 20000 miles because the foam filter gets saturated with oil and then it will drip occasionaly, but that's it, no other problems so far!
I have a '63 327 in a car, I popped a rubber gromment in the road draft hole on the back of the block, and stuck a PCV in there - the air enters the fill tube breather. Works great.
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